Mine's 77.59% and I really don't think that you can assess whether that's good or bad unless you know what the images are getting rejected for.
At one point (not the beginning, when I got bucket loads of stuff rejected as I didn't understand their standards) I was trying hard only to submit things I thought they'd accept, but there were several problems with that.
One is that other sites - SS for example - are much more willing to accept heavily Photoshopped images. Two of my recent hot sellers there (from this spring) were rejected by IS (overfiltering). My most recent Editor's Choice image at DT was rejected by IS for overfiltering and I gave IS a semi-filtered image that I don't think has anything like the impact (and in retrospect I shouldn't have done that - I generally don't resubmit if they reject).
Two is that I'm then boxing my photography/image creation in by iStock's standards, and I don't want to do that. IS has every right to set whatever criteria they want for acceptance. I didn't want to continue down the path of paying so much attention to that that I changed some things that matter to me about what I create.
Three is that once in a while, even after all this time, IS surprises me and accepts something I thought they'd reject.
Having created an image for multiple sites, I see no reason not to spin the roulette wheel at IS and see what happens.
